Spear Key

The Spear Key as a cube

The Spear Key (Japanese: やりのカギSpear Key) is a special artifact in the anime. It is a powerful object capable of locating ancient artifacts. With the Spear Key having such effects, it was retrieved by Team Galactic who used it in their various schemes.

In Gateway to Ruin!, the Spear Key was used by Saturn and Charon to find some ruins in Mt. Coronet. When it was found, the Spear Key did not react to it indicating that those were the wrong ruins, and thus they retreated.

In Unlocking the Red Chain of Events!, Saturn used the key at some ruins on Mt. Coronet. The Spear Key reacted, indicating they had finally found the Spear Pillar. In Battle Finale of Legend!, Cyrus uses the key to open these ruins, revealing a staircase leading to the Spear Pillar. After Team Galactic was defeated and Dialga and Palkia returned to their dimensions, the Adamant and Lustrous Orbs were retrieved, but the Spear Key has seemingly disappeared.

Trivia

Its name is a very obvious reference to the Spear Pillar, indicating that the two share a connection.

The three plates used to summon the Spear Key refer to Dialga and Palkia: the Splash Plate to Palkia's Water-type, the Iron Plate to Dialga's Steel-type, and the Draco Plate to the Dragon-type that both Pokémon are.